1. Field of the Invention
The present invention relates generally to a workpiece handling device, and more particularly, to a hydraulically or pneumatically operated mechanical wafer clamp for securing a substrate to a substrate handling device in a processing system.
2. Background of the Invention
Modern semiconductor processing systems include cluster tools which integrate a number of process chambers together in order to perform several sequential processing steps without removing the substrate from a highly controlled processing environment. These chambers may include, for example, degas chambers, substrate preconditioning chambers, cooldown chambers, transfer chambers, chemical vapor deposition chambers, physical vapor deposition chambers and etch chambers. The combination of chambers in a cluster tool, as well as the operating conditions and parameters under which those chambers are run, are selected to fabricate specific structures using a specific process recipe and process flow.
Once the cluster tool has been set up with a desired set of chambers and auxiliary equipment for performing certain process steps, the cluster tool will typically process a large number of substrates by continuously passing them through a series of chambers and process steps. The process recipes and sequences will typically be programmed into a microprocessor controller that will direct, control and monitor the processing of each substrate through the cluster tool. Once an entire cassette of wafers has been successfully processed through the cluster tool, the cassette may be moved to another cluster tool or stand alone tool, such as a chemical mechanical polisher, for further processing.
Typical cluster tools process one substrate at a time by passing the substrate through a series of process chambers that are each designed to process a single substrate at a time. However, more recent designs have incorporated a parallel processing structure whereby two substrates are processed at a time. In these dual systems, the robot has a pair of spaced parallel blades that pass the wafers through a series of parallel processing chambers. Each of the processing chambers is constructed to accommodate and process two wafers at a time. In this way, throughput of substrates in the cluster tool is effectively doubled. On exemplary fabrication system is the cluster tool shown in U.S. patent application Ser. No. 08/752,471, entitled xe2x80x9cDual Blade Robot,xe2x80x9d filed on Nov. 18, 1996, now U.S. Pat. No. 5,838,121 and which is incorporated herein by reference.
Substrate throughput in a cluster tool can be improved by increasing the speed of the wafer handling robot positioned in the transfer chamber. As the robot speed and acceleration increase, the amount of time spent handling each substrate and delivering each substrate to its next destination is decreased. However, the desire for speed must be balanced against the possibility of damaging the substrate or the films formed thereon. If a robot moves a substrate too abruptly, or rotates the wafer blade too fast, then the wafer may slide off the blade, potentially damaging the wafer, the chamber and/or the robot. Further, sliding movements of the substrate on the wafer blade may create contaminants, which if received on a substrate, can contaminate the substrate and the devices formed thereon. In addition, movement of the substrate on the wafer blade may cause substantial misalignment of the substrate that may result in inaccurate processing or even additional particle generation when the substrate is later aligned on the support member in the chamber.
Conventional robot designs rely on frictional forces that are present between the bottom surface of a wafer and the top surface of the wafer blade to prevent slippage of the wafer. The robot blade typically includes a wafer bridge on the distal end of the wafer blade and on the base of the blade to confine the wafer between the two ends of the blade. However, the wafer bridge at both the base and the distal end do not extend around the sides of the blade, and therefore, do very little to prevent the wafer from slipping laterally on the blade. Furthermore, the wafers are not always perfectly positioned against the bridge and movement or high rotational speeds may throw the wafer against one of the bridges and cause damage to the wafer or cause the wafer to slip over the bridge and/or off the blade. The total resistance due to friction is easily exceeded by the inertia of the wafer during rapid rotation or extension of the robot. However, this low coefficient of friction is typically relied upon when determining the speed at which a robot rotates.
patent application Ser. No. 08/801,076, entitled xe2x80x9cMechanically Clamping Robot Wrist,xe2x80x9d filed on Feb. 14, 1997, now U.S. Pat. No. 5,955,858 which is hereby incorporated by reference, further discusses the problem of wafer slippage on a robot blade and provides a mechanical clamping device to secure a wafer to the blade. The mechanical device relies on springs or flexure assemblies to clamp a wafer on a blade and is actuated by relative movement between the arms forming the linkage of the robot. While this is one solution, the design requires a relatively complex assembly to achieve clamping of a wafer.
Therefore, there is a need for a workpiece handling device which utilizes a simple and cost-effective wafer handling clamp to secure wafers during movement in a processing system.
The present invention is generally directed to a wafer clamping mechanism for retaining a wafer on a wafer handling robot. In one aspect, the wafer clamping mechanism comprises an actuation assembly mounted to the wafer handling robot proximate the wafer seat and a remote fluid source coupled to the actuation assembly through a fluid conduit for engaging the actuation assembly. The actuation assembly is adapted to engage a wafer with radial clamping forces on at least a portion of the edge of the wafer.
In one aspect, the clamping mechanism may be a fluid cylinder clamping mechanism, which itself further comprises: a fluid cylinder within a housing of the actuation assembly in fluid communication with the source of fluid pressure; a piston disposed within and adapted to reciprocate within the fluid cylinder in response to fluid pressure within the fluid cylinder; a piston rod affixed to and extending from the piston in a direction generally towards the wafer; and a clamping arm affixed to the housing and normally biased generally away from the wafer. In this aspect, the rod may be adapted to engage the clamping arm and bias the clamping arm towards the wafer to exert radial clamping forces on the wafer upon reciprocation of the piston. The wafer is retained with a clamping force sufficient to retain the wafer but insufficient to deform the wafer.
In another aspect, the clamping mechanism may be a bladder clamping mechanism comprising a chamber formed in the housing body of the actuation assembly; a bladder disposed within the chamber and in fluid communication with the source of fluid pressure; and a clamping arm affixed to the housing body and normally biased generally away from the wafer. In this aspect, the bladder is adapted to engage the clamping arm and to bias the clamping arm towards the wafer to exert radial clamping forces when the bladder is expanded or inflated in response to fluid pressure. The wafer is retained with a clamping force sufficient to retain the wafer but insufficient to deform the wafer.
In yet another aspect, the clamping mechanism may be a bellows clamping mechanism which comprises a chamber within a housing body of the actuation assembly; a clamping arm affixed to the housing and normally biased generally away from the wafer; and a bellows disposed in and affixed to the housing body chamber and having a front volume in fluid communication with the source of fluid pressure. In this aspect, the bellows has a piston affixed to an end of the bellows generally towards the clamping arm. The bellows piston is adapted to reciprocate within the housing chamber in response to fluid pressure within the front volume within the bellows and to engage the clamping arm and to bias the clamping arm towards the wafer to exert radial clamping forces on the wafer upon reciprocation of the bellows piston. The wafer is retained with a clamping force sufficient to retain the wafer but insufficient to deform the wafer.
In still another aspect, the clamping mechanism comprises a dual bellows leaf spring clamping mechanism having a manifold having a fluid passageway therein; a first bellows affixed to the manifold and having a bellows chamber in fluid communication with the manifold passageway; a second bellows affixed to the manifold and having a bellows chamber in fluid communication with the manifold passageway; and a flexure member attached to one or more bellows actuation plates affixed to opposing ends of the first and second bellows. In this aspect, the flexure member forms an arc in a direction generally towards the wafer. The flexure member is also normally biased outward to extend the first and second bellows away from the manifold so that an apogee portion of the flexure member is withdrawn away from the wafer. The bellows actuation plates are further adapted to retract towards the housing in response to fluid pressure provided in the housing to extend the apogee portion of the flexure member in a direction generally towards the wafer to exert radial clamping forces on the wafer. In this aspect, the source of fluid pressure may be a vacuum pressure source and the flexure member may be a leaf spring.
In another aspect, the invention provides a method of retaining and releasing a wafer on a wafer handling robot. The method comprises the steps of providing a clamping mechanism proximate an outer edge of the wafer responsive to fluid pressure; providing fluid pressure to the clamping mechanism so that a clamping arm extends towards the edge of the wafer to be retained; and releasing the wafer by removing fluid pressure from the clamping mechanism so that the clamping arm retracts from the edge of the wafer. In this aspect of the invention, the wafer is retained with a clamping force sufficient to retain the wafer but insufficient to deform the wafer.